Method of and apparatus for machining articles

ABSTRACT

A beveled edge is formed on a very thin, cylindrical silicon wafer by depositing a quantity of diamond lapping material on the upper peripheral edge portion of the wafer and bringing a rotating, hard steel tool down into engagement with the edge portion of the wafer, the tool having a water-engaging face which is beveled at the desired angle.

United States Patent Donald F. Stahr Johnstown;

Rudolph M. Yandrick, Indiana, both of, Pa. 829,961

June 3, 1969 Sept. 7, 1971 FMC Corporation San Jose, Calif.

Inventors Appl. No. Filed Patented Assignee METHOD OF AND APPARATUS FOR MACHINING ARTICLES 10 Claims, 4 Drawing Figs.

US. Cl 51/125, 51/281 SF, 51/283 Int. Cl B24b 9/06 Field of Search 51/54, 56,

References Cited UNITED STATES PATENTS 1,048,059 12/1912 Foppiano 408/17 1,241,236 9/1917 Mathy 51/125 2,395,700 2/1946 Walker.... 51/216 3,158,968 12/1964 Ness 51/125 Primary Examiner-Granville Y. Custer, Jr. Attorneys F. W. Anderson and C. E. Tripp ABSTRACT: A beveled edge is formed on a very thin, cylindrical silicon wafer by depositing a quantity of diamond lapping material on the upper peripheral edge portion of the wafer and bringing a rotating, hard steel tool down into engagement with the edge portion of the wafer, the tool having a water-engaging face which is beveled at the desired angle.

PATENTEU'SEP van 3503; 039

INVENTORS DONALD F. STAHR IE I G 4:] I BY)? Ruuoum unuomcx ATTORNEYS METHOD OF AND APPARATUS FOR MACHINING ARTICLES BACKGROUND OF THE INVENTION In electronic control mechanisms circular silicon wafers are used which have a thickness in the range of from about 0.009 inch to 0.015 inch and a diameter in the range of from approximately 0.75 inch to 1.50 inch. In order to reduce the electric field at the surface of the wafer to below that of the bulk material and obtain stable operation of silicon devices at voltages exceeding 800 volts it is necessary to provide a smooth uniform bevel at the periphery of each wafer.

At present the beveling of silicon is usually accomplished by means of the use of a stream of air-blasted abrasive, by grinding with diamond tools, or by cutting with an electric discharge machine. Each of these methods have detrimental aspects such as rough, nonuniform surface, poor reproducibility, pitting or tearing of the silicon or exorbitant cost.

Accordingly it is an object of the present invention to provide an improved method of forming a bevel on silicon.

Another object is to provide an improved method of beveling silicon wafers by means of inexpensive tools, materials and machinery.

A further object is to provide a simple efficient mechanism for forming predetermined contours on relatively hard surfaces such as the surface of a silicon wafer.

Other and further objects will be apparent to one skilled in the art from the following description taken in connection with the accompanying drawings.

SUMMARY OF THE INVENTION The present invention provides a method and apparatus for forming a desired contour on a relatively hard piece of material, such as a thin cylindrical silicon wafer, by securing the wafer to a flat support; depositing a small amount of a diamond lapping material on the peripheral upper surface of the wafer; bringing a hard steel tool, that has a beveled lower surface, down onto the wafer with a light pressure so that the beveled lower surface of the tool engages the peripheral surface of the wafer; and rotating the tool, as it is moved into engagement with the wafer, at a speed in the range of approximately 2,500 to 5,000 r.p.m.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic side elevation of apparatus for carrying out the method of the present invention.

FIG. 2 is a diagrammatic perspective of a portion of the mechanism of FIG. 1 and particularly showing a silicon wafer before its edge has been beveled.

FIG. 3 is a fragmentary diagrammatic side elevation of a portion of the mechanism of FIG. I, particularly showing a circular silicon wafer, the upper peripheral edge of which has already been beveled.

FIG. 4 is an enlarged vertical section taken along a diameter of the circular silicon wafer and of the generally cylindrical wafer-engaging tool, showing the tool in operative engage ment with the wafer and the material disposed between the tool and the wafer.

DESCRIPTION OF A PREFERRED EMBODIMENT In FIG. 1 the reference numeral indicates a machine tool of the drill press type wherein a rigid post 12 projects upwardly from a rigid base 14. A support arm 16 has one end 16a slidably disposed on the post 12 and, at its other end 16b, the arm 16 rotatably supports a vertical spindle 18. An electric motor 20, which is mounted on support arm 16, is in driving engagement with a reduced diameter portion 18a of the spindle 18 through a belt and pulley drive 21.

The support arm 16 is connected by a rigid member 23 to a collar 24 which extends around the post 12 and is connected thereto by an elevating mechanism 25 which includes a handle 26 and a rack and pinion mechanism (not shown) which is disposed in the collar 24 and is operatively connected between the handle and the post 12 to cause the collar and the connected support arm 16 to be lowered when the handle is rotated clockwise about the pivot axis X from the FIG. I position.

A beveling tool head 30, which is made of hard tool steel and is removably mounted in a chuck 32 carried by the spindle 18, has a recessed lower surface which is defined by a frustoconical wall 34. The wall is tapered inwardly at an angle Y which is 6 or less and it is this angle that determines the angle that will be formed on the peripheral edge of the circular silicon wafer.

To initiate a beveling operation, a circular silicon wafer W is attached in face-to-face contact with the flat upper surface of a rigid support plate 40 which may be made of steel or aluminum. The attachment of the wafer to plate 40 is made by melting a quantity of low-melting wax on the plate 40, placing the wafer W on the wax in a predetermined location on the plate, and allowing the wax to cool. The plate is then mounted by means of an alignment jig in a predetermined position on the base so that the peripheral edge of the wafer W is directly below the beveled wall 34 of the tool head 30. A ribbon of diamond lapping material M is placed on the upper surface of the wafer adjacent to the outer peripheral edge. The motor 20 is energized to rotate the head 30, and the handle 26 is swung clockwise to lower the head into engagement with the wafer.

One form of diamond lapping material that has been found to be satisfactory for beveling silicon wafers with the apparatus of the present invention is marketed by Kay Industrial Diamond Co. of Brooklyn, N.Y. under the designation of Kay Industrial Diamond 015 NBS-natural diamond8.22 micron grit size. The abrasive material is prepared as an oily paste and supplied in a tube or syringe so that a ribbon of the material can be disposed on the surface to be beveled.

The tool head is brought into contact with the wafer under a light pressure that is sufficient to maintain a constant contact with the wafer. Under the pressure of the rotating head and the action of the diamond lapping material, the peripheral edge of the wafer is brought to a beveled configuration that corresponds substantially to the configuration of the wall 34 of the head 30 as indicated in FIG. 4.

When the diameter and thickness of the wafers being beveled are known, as well as the desired bevel angle; the inner diametral dimension D (FIG. 3) of the finished wafer is known. Accordingly, a surface gauge in the form of a cylindrical block having a diameter equal to the dimension D may be used to check the wafer. This checking is accomplished by placing the gauge on top of the wafer and comparing visually the dimension D and the diameter of the gauge. A final check can be made more precise measuring instruments. While a complete beveling operation may be accomplished by a single application of the rotating head to the wafer, a series of applications may be necessary.

After a beveling operation, the tool head 30, the wafer W, and the support plate 40 are wiped off with a sheet of paper to which the diamond lapping material will cling. When a batch of paper sheets have been accumulated, the sheets are burned and the residue from the burning is collected. From this residue diamond abrasive material is separated and it has been found that approximately percent of the original diamond material can be recovered. This recovery of the material makes the beveling operation of the present invention relatively inexpensive.

It should also be noted that, since the tool head 30 rotates relatively slowly compared to a 10,000-15 ,000 rpm. diamond tool used for beveling operations, the possibility of breakage of the wafers if greatly reduced.

When a silicon wafer is beveled in accordance with the method of the present invention an 8-10 micron finish can be obtained on the wafer whereas other beveling methods produce 25-400 micron finishes.

As previously noted, the wafer is mounted in a fixed predetermined position on the support 14 so that the tool will engage its peripheral portion. in practice; the means for locating the circular wafer relative to the support could be a guide circle inscribed on the support 14 directly under the tool. It will be recognized that the dull-press-type structure disclosed is particularly adapted for controlling the pressure that is applied to the wafer since it is hand operated.

While it has been found that the angle of bevel should not exceed 6 for silicon wafers having a thickness up to 0.015 inch, it is contemplated that greater angles can be formed on other types of articles such as articles that are thicker or are of a different material.

The apparatus described above is obviously very inexpensive compared to the apparatus used in other methods.

From the foregoing description it will be apparent that the present invention provides a simple, inexpensive method and apparatus for producing a bevel of predetermined angle on a silicon wafer, Further, it is evident that while the use of lapping material and a rotating pressure-applying tool have been used for polishing flat metal surfaces, the present invention embodies the first use of such apparatus and material for changing the configuration of an object from one geometric shape to another.

It will be noted in FIG. 4 that the lower surface of tool 30 is inclined, internal surface while the bevel that is eventually formed on the wafer is an inclined outer surface. It will be evident that if a concave surface is to be formed on the wafer, the mating portion of the tool would have a convex configuration. Thus, in effect, the configuration of the tool surface is reversed" from the desired configuration and, accordingly, in the following claims the term reverse the relative orientations of the surface of the tool and the desired surface. This of course is a further distinction over the normal lapping operation wherein a flat lap surface engages a flat surface, not to change its configuration, but to polish it.

It will be understood that modifications and variations may be effected without departing from the scope of the present.

Having described the invention what is claimed as new and for which Letters Patent is desired is:

1. A method of forming a bevel on the peripheral edge of a circular article, comprising the steps of mounting the article in fixed position; disposing a quantity of abrasive material on the surface extending around the periphery of the article where the bevel is to be formed; and engaging the abrasive with a rapidly moving circular tool surface, which has a configuration the reverse of the desired configuration and which is rotating about its own axis; to force the abrasive into contact with the surface of the article until the desired configuration is formed on the article surface.

2. A method according to claim 1 wherein said tool surface is rotated at a speed in the range of approximately 2,500 to 5 ,000 r.p.m.

3. For use in forming a bevel on the peripheral edge portion of a circular article, the combination of a support, means for securing the article in fixed position on said support, a rotary tool mounted adjacent said support, means defining a circular inclined contact surface on said tool, said surface being generated about the axis of rotation of said tool, an abrasive adapted to be disposed on the peripheral edge portion to be beveled, means for moving said inclined contact surface into engagement with the abrasive on the article to force the abrasive into pressurized contact with said peripheral edge portion, and means for rotating said tool while said contact surface is in pressure engagement with the abrasive.

4. For use in the forming of a bevel on the periphery of a circular silicon wafer the combination of a support, means for securing the wafer on said support in fixed position, a tool having a lower circular contact surface that is beveled with an orientation reversed relative to the orientation of the bevel to be formed on the wafer, means mounting said tool above said support with the beveled surface of the tool aligned with the eripheral portion of the wafer, and with the axis of the circuar contact surface of said tool being in substantial alignment with the axis of the circular wafer, means for rotating said tool about its axis, a diamond abrasive adapted to be disposed on the peripheral portion of the wafer facing the circular tool surface, and means for moving said rotating tool surface downwardly into engagement with the abrasive on the wafer to press the abrasive into abrading contact with the wafer.

5. The combination of claim 4 wherein the bevel on said tool surface is equal to or less than 6.

6. The combination of claim 4 wherein said tool surface is made of tool steel.

7. The combination of claim 4 wherein said means for rotating said tool includes means for maintaining the speed of said tool in the range of from approximately 2,500 r.p.m. to approximately 5,000 r.p.m.

8. The combination of claim 4 wherein said diamond abrasive has a pastelike consistency adapting the abrasive to be disposed on the peripheral portion of the wafer in a ribbonlike form.

9. The combination of claim 4 wherein said means for moving said tool surface downwardly is adapted for applying a light pressure to the wafer through the tool as the tool rotates.

10. A method of forming a surface of desired configuration on an article comprising the steps of mounting the article in fixed position; disposing a quantity of diamond lapping material with a pastelike consistency on the surface to be worked; engaging the abrasive with a rapidly moving tool surface having a configuration that is substantially the reverse of the desired configuration to force the abrasive into contact with the surface of the article; maintaining the pressure of said tool surface against said abrasive until the desired configuration is formed on the article surface; wiping the abrasive material from the tool surface, the workpiece and associated fixtures by means of an inflammable wiper member; and burning the wiper member to provide a residue from which diamond material may be separated.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,603,039 Dated September 7, l 9 'Z l WELLiIAHLRndNRWNDRIL It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

Abstract Line 6, "water" should be -wafer-. Column 2 line 33, "0" should be Signed and sealed this 20th day of June 1972.

(SEAL) Attest:

EDL SARD M.FLETC.IEE,JR. ROBERT GOTTSCHALK Attestlng Officer Commissioner of Patents 

1. A method of forming a bevel on the peripheral edge of a circular article, comprising the steps of mounting the article in fixed position; disposing a quantity of abrasive material on the surface extending around the periphery of the article where the bevel is to be formed; and engaging the abrasive with a rapidly moving circular tool surface, which has a configuration the reverse of the desired configuration and which is rotating about its own axis; to force the abrasive into contact with the surface of the article until the desired configuration is formed on the article surface.
 2. A method according to claim 1 wherein said tool surface is rotated at a speed in the range of approximately 2,500 to 5,000 r.p.m.
 3. For use in forming a bevel on the peripheral edge portion of a circular article, the combination of a support, means for securIng the article in fixed position on said support, a rotary tool mounted adjacent said support, means defining a circular inclined contact surface on said tool, said surface being generated about the axis of rotation of said tool, an abrasive adapted to be disposed on the peripheral edge portion to be beveled, means for moving said inclined contact surface into engagement with the abrasive on the article to force the abrasive into pressurized contact with said peripheral edge portion, and means for rotating said tool while said contact surface is in pressure engagement with the abrasive.
 4. For use in the forming of a bevel on the periphery of a circular silicon wafer the combination of a support, means for securing the wafer on said support in fixed position, a tool having a lower circular contact surface that is beveled with an orientation reversed relative to the orientation of the bevel to be formed on the wafer, means mounting said tool above said support with the beveled surface of the tool aligned with the peripheral portion of the wafer, and with the axis of the circular contact surface of said tool being in substantial alignment with the axis of the circular wafer, means for rotating said tool about its axis, a diamond abrasive adapted to be disposed on the peripheral portion of the wafer facing the circular tool surface, and means for moving said rotating tool surface downwardly into engagement with the abrasive on the wafer to press the abrasive into abrading contact with the wafer.
 5. The combination of claim 4 wherein the bevel on said tool surface is equal to or less than 6*.
 6. The combination of claim 4 wherein said tool surface is made of tool steel.
 7. The combination of claim 4 wherein said means for rotating said tool includes means for maintaining the speed of said tool in the range of from approximately 2,500 r.p.m. to approximately 5,000 r.p.m.
 8. The combination of claim 4 wherein said diamond abrasive has a pastelike consistency adapting the abrasive to be disposed on the peripheral portion of the wafer in a ribbonlike form.
 9. The combination of claim 4 wherein said means for moving said tool surface downwardly is adapted for applying a light pressure to the wafer through the tool as the tool rotates.
 10. A method of forming a surface of desired configuration on an article comprising the steps of mounting the article in fixed position; disposing a quantity of diamond lapping material with a pastelike consistency on the surface to be worked; engaging the abrasive with a rapidly moving tool surface having a configuration that is substantially the reverse of the desired configuration to force the abrasive into contact with the surface of the article; maintaining the pressure of said tool surface against said abrasive until the desired configuration is formed on the article surface; wiping the abrasive material from the tool surface, the workpiece and associated fixtures by means of an inflammable wiper member; and burning the wiper member to provide a residue from which diamond material may be separated. 